Good read but very tin hatty. There were some pretty cool ideas in the book but the scenario is quite extreme as are the situations they find themselves in.
For me, I'll hopefully be in the mountains already once we find the land we're looking for, but until then we have BOB's ready to go in case we MUST leave our house, but since I cannot load up enough supplies on my back or in my vehicles for more than a few weeks I plan on staying put as long as possible, and if I have to head out then I'll probably head north and east, not west. Everybody and their brother who ever thinks of bugging out picks the mountains, so that is a lot of folks to get through. What's worst is that most people don't know how to survive the mountains and will get desperate fast, and that's one more factor to contend with.
I don't agree that the mountain towns will block their roads, there will be a compassion factor in the first 24-48 hours as well as the fact that nobody is likely to get that organized that fast, the problem will be gridlock. It only takes a couple of accidents or broken down vehicles to block the major arteries into the mountains and then you are on foot and no better off than you were before.
I'll take my Jeep north and east, because I can't drive straight up a mountain but I can drive over nearly any terrain (including yards, fields, whatever) to get out of the city that way and there will be far fewer people bugging out to the rich farming lands of Nebraska or Kansas than in the mountains. I'll find a place that is defensible with folks who are less tactically experienced and need someone like me to help defend their homestead in exchange for food and shelter.
But no matter what it's a challenge, I live in Denver and how hard do you think THAT'S going to be getting out of town?!?!?! The mountains used to be my first choice and I've spend years refining my survival skills for our mountains in particular, but in the end I know it's the toughest choice possible and will likely go elsewhere (maybe circle back to them after initial die offs).